The warning (No method declared with Objective-C selector 'swipedLeft:') should be your first clue that there's a problem...
If you use this code in Swift 3, the left-swipe will result in an error like this:
2016-12-24 08:15:12.645 SpriteSimpleGame[65853:2987246] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[SpriteSimpleGame.GameScene swipedLeft:]: unrecognized selector sent to instance 0x7fb99e4101f0'
Worst of all, examples like this are all over the place because leaving out the colon results in a similar error.
Thanks to this answer I learned that what you want instead is this:
let swipeLeft = UISwipeGestureRecognizer(